linux-kernel - [RFC PATCH v2 05/10] KVM: x86: lapic: don't allow to change APIC ID when apic acceleration is enabled

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Date:   Thu, 21 Apr 2022 08:12:39 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        intel-gfx@...ts.freedesktop.org,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Zhi Wang <zhi.a.wang@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        intel-gvt-dev@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, x86@...nel.org,
        David Airlie <airlied@...ux.ie>,
        Sean Christopherson <seanjc@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <joro@...tes.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [RFC PATCH v2 05/10] KVM: x86: lapic: don't allow to change APIC ID when apic acceleration is enabled

No normal guest has any reason to change physical APIC IDs, and
allowing this introduces bugs into APIC acceleration code.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/lapic.c | 28 +++++++++++++++++++++++-----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 66b0eb0bda94e..56996aeca9881 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2046,10 +2046,20 @@ static int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
 
 	switch (reg) {
 	case APIC_ID:		/* Local APIC ID */
-		if (!apic_x2apic_mode(apic))
-			kvm_apic_set_xapic_id(apic, val >> 24);
-		else
+		if (apic_x2apic_mode(apic)) {
 			ret = 1;
+			break;
+		}
+		/*
+		 * Don't allow setting APIC ID with any APIC acceleration
+		 * enabled to avoid unexpected issues
+		 */
+		if (enable_apicv && ((val >> 24) != apic->vcpu->vcpu_id)) {
+			kvm_vm_bugged(apic->vcpu->kvm);
+			break;
+		}
+
+		kvm_apic_set_xapic_id(apic, val >> 24);
 		break;
 
 	case APIC_TASKPRI:
@@ -2617,8 +2627,16 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
 static int kvm_apic_state_fixup(struct kvm_vcpu *vcpu,
 		struct kvm_lapic_state *s, bool set)
 {
-	if (apic_x2apic_mode(vcpu->arch.apic)) {
-		u32 *id = (u32 *)(s->regs + APIC_ID);
+	u32 *id = (u32 *)(s->regs + APIC_ID);
+
+	if (!apic_x2apic_mode(vcpu->arch.apic)) {
+		/* Don't allow setting APIC ID with any APIC acceleration
+		 * enabled to avoid unexpected issues
+		 */
+		if (enable_apicv && (*id >> 24) != vcpu->vcpu_id)
+			return -EINVAL;
+	} else {
+
 		u32 *ldr = (u32 *)(s->regs + APIC_LDR);
 		u64 icr;
 
-- 
2.26.3